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Ecoscenario: Saguaro National Park 4/16/03 3:23 PM desert plants. BIOTIC DATA All ecosystems depend on the Sun for energy, but organisms in the Sonoran Desert survive in spite of the Sun and its intense heat. Plant and animal life is abundant in Saguaro National Park and throughout the Sonoran Desert. Organisms are adapted to this harsh environment. Despite the intense sunlight, the growing season in the desert is short because of the lack of water. The most dominant organism is the large saguaro cactus. It can grow up to 15 meters (49 feet) tall. Its huge humanlike shape dwarfs everything else, including humans. The time needed by the cactus to reach those amazing heights can exceed 100 years. A saguaro cactus may grow only 0.6 centimeter (0.25 inch) during its first year and may need as many as 30 years to reach 1 meter (3 feet). It begins to flower after about 55 years. The distinctive arms do not appear until the cactus is between 50 and 100 years old. file:///Ecoscenario/saguaro/content.html Page 4 of 12
Ecoscenario: Saguaro National Park 4/16/03 3:23 PM Art Explosion Humans are dwarfed by giant saguaro cactus. Courtesy of Anne Marie Gearhart Thorns grow along the pleats of a saguaro cactus. During the rainy season, saguaros absorb huge amounts of water. Their accordian shape expands to hold more water, and a thick, waxy epidermis slows transpiration. Mixed with the saguaros are mesquite trees, ocotillo, creosote bushes, barrel cactus, prickly pear, and grama grass. Each has its own adaptation for collecting and storing water. Cacti photosynthesize with the epidermis layer of their stems. Thorns are leaves that have shrunk over time. The thorns also protect cacti by discouraging animals from browsing on their water-rich tissues. Some long-lived plants, such as mesquite trees and creosote bushes, have exceptionally long roots to reach water deep in the earth. Other plants, including prickly pear and saguaro cactus, have shallow, netlike roots to help capture water from the brief rains. Soils in the desert are generally poor. In many places the ground is covered with a thin rocky layer called desert pavement. It is a layer of pebbles and small rocks. All the surrounding sand has been blown or washed away, leaving a surface that looks as if it was placed there on purpose. Desert pavement may take thousands of years to form. Directly beneath the layer of pebbles is a thin layer of soil that contains organic material. This layer is rich in cyanobacteria (blue-green algae), and may support substantial growths of algae, lichens, and mosses. file:///Ecoscenario/saguaro/content.html Page 5 of 12
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Ecoscenarios Combined - FOSSweb

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